Where downhole tools are used to accomplish stationary tasks (e.g., well-logging or well-completion tasks) via suspension lines (e.g., wirelines or slicklines) in a wellbore, the depth of the suspended tool string is of considerable importance. For example, in well-logging processes, it is often necessary to take corresponding measurements over multiple runs at the same depth position within the wellbore. Additionally, logs from different wellbores may be depth-matched for comparison. Thus, errors in depth measurement of the tool string are detrimental to data interpretation. Moreover, performing completion processes at the wrong depth can result in excessive fluid production in the wellbore and/or entirely bypassing a particular zone of interest in the wellbore.
To locate the tool string in a substantially vertical wellbore, one conventional process is to initially drop the tool string below the intended depth and subsequently pull the tool string up to the target depth by a winch, so that the cable is held in tension. Yet, when the winch is stopped at the target depth, the tool string continues to move on the suspension line upward out of the wellbore. This phenomenon is known as “creep.” Failure to account for creep causes downhole tool operations to be conducted at an incorrect depth.